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Pretreatment of Wool - 2
Wool Scouring with organic solvent:
The wool cleaning system involves the use of a
non-aqueous solvent (tri-chloro-ethylene) and does not use any water in
the washing process.
The technique is reported to be applicable to
any kind of wool. Scarcity of water is cost likely the main driving force
for the implementation of this technique.
The use of water is avoided in the actual wool
cleaning process. The only source of water emission is moisture introduced
with the wool, steam used in vacuum ejectors and moisture recovered from
sir drawn in to the equipment. This water is treated in two steps
comprising a solvent air stripping unit and a residual solvent destruction
unit. The residual traces destroyed using a free radical process based in
the Fenton Reaction (iron and hydrogen peroxide).
Advantages of Organic Solvent Scouring:
Since pesticides adhere strongly to the
solvent and are discharged with the grease, the clean wool is reported to
be pesticide free. This has positive implications for the downstream
processes where wool is finished.
Another positive effect of this technique is
the reduction in energy consumption due to the low latent heat of
evaporation of the organic solvent compared to water.
2. Carbonizing:
 Carbonizing
is a chemical treatment used to remove the vegetable impurities, which may
remain on scoured wool after technical treatments.
The Textile substrates
treated are:
- Floc / loose fiber (only fiber used to
produce fine fabric for garments, so called worsted fabrics).
- Fabric ( not applied in the carpet
sector).
Carbonizing may be practiced on fabrics before
or after felting (depending on the quality) as well as before or after
coloring. Carbonizing of raw fiber is rare as the material is then
difficult to dye (e.g. after chrome dyes cannot be used or different
carbonized yarns will lead to irregularities in the color affinity of the
woven fabric).
Synthetic fibers (PA, PAC, PES etc) which are
not damaged by the treatment, can also be carbonized; the
Carbonising treatment can also be applied on wool blends.
The principle of the process of treatment
using a strong acid (mainly) Sulphuric acid to transform cellulose in to
mechanically removable hydrocellulose. The best effects are obtained with
good pre-washed and dried material. Some processes there fore recommend
pre-washing or impregnating the fabric with perchloroethylene.
The classical Carbonising
treatment of fabric usually involves the following operational steps:
- Impregnated with Sulphuric acid (
6-9 %of acid).
- Squeezing, exhaustion or whizzing of
the surplus acid solution (5% solution relative to fabric weight may
remain).
- baking at 60 to 90C to concentrate
the acid
- baking at 105 to 130C (Carbonizing).
- Rumbling and rapping (mechanical
treatments) to remove the carbonized particles.
- Washing and neutralizing with dilute
Ammonia Solution.
The use of wetting agents leads to thorough
wetting of the greige goods and reduces impregnation time. To avoid damage
of the wool, an excess of sodium carbonate may be added to the
neutralizing liquor.
3. Scouring and Desizing:
The combined treatment of scouring and
desizing removes lubricants that are also called lubricating oils, rag
pulling or batching oils and in some cases this process also removes
sizing agents from woolen yarns and fabrics.
Typical substances that must be removed by
scouring wool can be classified as:-
- Soluble in water
- Insoluble in water, but able to
emulsify with detergents.
- Insoluble in water and
non/poorly emulsifying with detergents. These substances are
only removed with organic solvent.
The washing will therefore occur with water or
with organic solvent (dry cleaning)
Washing (Scouring) solution for wool:-
Water washing: Sodium carbonate or
bi-carbonate solution (neutral or weakly alkaline conditions).
Dry Cleaning: Perchloroethylene (most widely
used), water and detergent (optional).
Worsted (or combed) wool under goes short
water washing (10 to 20 dipping) with strong non-ionic detergents. The
treatment usually occurs under same machine used for subsequent dyeing.
Colored worsted wool is first washed with an ammoniac solution to remove
non-fixed dyes. The treatment is finished with a washing in a solution of
formic acid and anti-electrostatics.
Woven or knitted fabrics are commonly washed
not only to remove the lubricants but also to give the fabric a special
luster or handle. Further more the fabric is relieved from the tensions of
the proceeding knitting or weaving. Here too ammoniac solution may be used
to pre-wash the fabric.
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